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Thermomechanical

(CalculiX Solver)

The analysis type Thermomechanical allows the calculation of the structural and thermal behavior of one or multiple bodies at once. The thermal and structural result fields are not calculated simultaneously but sequentially in an iterative process where the results of a thermal step serve as input for the next structural step. The stress state of the structure depends accordingly on the structural constraints and loads as well as on the thermal expansion under thermal loads.

The results enable you to investigate the structural and thermal behavior of the structure as well the thermal influences on the structural load state of the domain. This is very interesting when dealing with solid bodies that are heated or cooled while constrained by bearings or similar constraints at the same time like for example thermal shrinkage during assembly processes.

Temperature change and stresses in globe valve

Temperature change and stresses in globe valve after a hot shock

In the following the different simulation settings you have to define are described in detail as well as the various options you can add.

Analysis Type

You can choose steady-sate if you want to calculate the steady-state behavior of the system comparable to the Static analysis and Steady-state heat transfer or transient if you want to take time dependent effects into consideration in a transient analysis.

Domain

In order to perform an analysis a given geometrical domain you have to discretize your model by creating a mesh out of it. Details of CAD handling and Meshing are described in the Pre-processing section.

After you assigned a mesh to the simulation you can add some optional domain-related settings and have a look on the mesh details. Please note that if you have an assembly of multiple bodies that are not fused together, you have to add Contacts if you want to build connections between those independent parts.

Model

In the model section everything that defines the physics of the simulation is specified e.g. material properties, boundary conditions etc. On the top level you can adapt some generic settings. For a Thermomechanical you can add a gravitational load for the whole domain.

Materials

In order to define the material properties of the whole domain, you have to assign exactly one material to every part. You can choose the material behavior describing the constitutive law that is used for the stress-strain relation and the density of the material. Please note that the density is used for volumetric loads e.g. gravitation. Inertia effects are only considered in dynamic simulations (Dynamic). Please see the Materials section for more details.

Initial Conditions

For a time dependent behaviour of a solid structure it is important to define the Initial Conditions carefully, since these values determine the solution of the analysis. In a transient analysis the displacement and velocity are handled the same way as in a Dynamic analysis. Therefore they need to be defined beforehand, as they determine the initial state of the domain before the loads and constraints are applied. Per default the displacement and velocity are initialized as zero length vector. Thus if you use the default values there will be no displacement and velocity in the initial state. Furthermore the temperature of a transient a analysis needs to be defined initially.It is set to room temperature (293.15 K) by default and is also provided for steady-state simulations for convergence reasons.

Boundary conditions

For a Thermomechanical analysis you may apply both structural as well as thermal boundary conditions:

Constraints and Loads (Boundary conditions)

You can define Constraints (Displacement boundary conditions) and Loads (Force boundary conditions). If you want to determine the position of a part of the domain, add at least one displacement constraint in every coordinate direction. Otherwise it is allowed to move freely in space. This is intended for e.g. drop tests.

In case of missing force boundary conditions (including gravitation), the geometry becomes load-free and apart from the prescribed displacement boundary conditions (constraints) no deformation will evolve. However, this might be intended to determine the strain distribution e.g. in pre-clamped structural components.

Constraint types (Displacement boundary conditions)

Load types (Force boundary conditions)

Temperature and Heat flux boundary conditions

You can define temperature and thermal load boundary conditions. If you provide a temperature boundary condition on an entity, the temperature value of all contained nodes is set to the given prescribed value. Thermal load boundary conditions define the heatflux into or out of the domain via different mechanisms. Note that a negative heat flux indicates a heat loss to the environment. As a temperature boundary condition prescribes the temperature value on a given part of the domain it is not possible to simultaneously add a thermal load on that part as it would be overconstrained in that case.

Temperature boundary condition types (Thermal Constraints)

Heat flux boundary condition types (Thermal Loads)

Numerics

Under numerics you can set the equation solver of your simulation. The choice highly influences the computational time and the required memory size of the simulation.

Simulation Control

The Simulation Control settings define the overall process of the calculation as for example the timestepping interval and the maximum time you want your simulation to run before it is automatically cancelled.

Solver

The described Thermomechanical analysis of the finite element code CalculiX Crunchix (CCX) is only available via the solver perspective. You may as well choose the finite element package Code_Aster for this analysis type (Thermomechanical analysis CA) using the standard Thermomechanical analysis from the physics perspective or via the solver perspective choosing Code_Aster as solver. See our Third-party software section for further information.

See our Third-party software section for further information.